This invention relates to the use of inertial navigation systems (INS) on vehicle such as trucks and tanks, in particular integrating INS with a mechanical odometer of Vehicle Motion Sensor (VMS) on the vehicle.
Current Inertial Navigation Systems (INS) models for odometer aiding assume the vehicle suspension is a rigid body. Odometer aided inertial systems create an integrated navigation solution. Because the inertial system is mounted on the vehicle body measuring the vehicle motion while the odometer measures motion of the chassis, the odometer aided inertial system attempts to estimate the orientation between the vehicle body and the vehicle chassis to correct for errors in the odometer. This inertial/odometer error model works well when the vehicle suspension system is rigid. A vehicle suspension system is rigid when there is a constant orientation between the vehicle body and vehicle chassis. An inertial/odometer error model xe2x80x9cworks wellxe2x80x9d when the integrated solution can estimate the relative orientation of the vehicle body to the vehicle chassis with a 0.08 degree or better accuracy. The assumption of constant relative orientation does not work well when the vehicle body moves significantly relative to the vehicle chassis. In some vehicles, this motion can be as much as two degrees. Significant errors in the odometer calibration occur when changes in this orientation are not modeled correctly. These errors in odometer calibration degrade the primary system outputs. Both vertical velocity and vertical position (altitude) are degraded because of the odometer modeling errors.
Additional error sources occur when the odometer is connected to a vehicle with tires that can deform as a function of vehicle loading. This deformation can occur when the vehicle is traveling up or down a hill, resulting in significant changes in odometer scale factor, on the order of one to two percent. These scale factor changes can result in poor position performance when the vehicle is traveling in a hilly terrain.
Present state of the art for odometer aided inertial systems models a vehicle suspension system as a rigid body. Odometer aided inertial systems create an integrated navigation solution. The integrated navigation solution contains data such as vehicle position, vehicle velocity and vehicle attitude. In addition to these primary system outputs, the odometer aided inertial system calibrates the odometer with an odometer error model. Because the inertial system is mounted on the vehicle body and the odometer measures motion of the chassis, the odometer aided inertial system attempts to estimate the orientation between the vehicle body and the vehicle chassis. The body of this vehicle is defined as the upper part of this vehicle containing the engine, occupants, ammunition, etc. The vehicle body rests upon the vehicle chassis which is defined as the under part of this vehicle consisting of the frame with axles and the wheels or tracks.
This inertial/odometer error model works well when the integrated solution can estimate the relative orientation of the vehicle body to the vehicle chassis with a 0.08 degree or better accuracy. The assumption of constant relative orientation does not work well when the vehicle body moves significantly relative to the vehicle chassis. In some vehicles, this motion can be as much as two degrees. Significant errors in the odometer calibration occur when changes in this orientation are not modeled correctly. These errors in odometer calibration degrade the primary system outputs. Both vertical velocity and vertical position (altitude) are degraded because of the odometer modeling errors. In additional, such attitude variations produce errors in calibration as explained below.
According to the invention, inertial sensor data from an INS, corrected by the Kalman filter via navigation state corrections, is integrated to form inertial position, velocity, and attitude. Inertial position represents the position of the vehicle on the earth. Inertial velocity represents the velocity of the vehicle with respect to the earth. Inertial attitude data describes the orientation of the vehicle body with respect to the earth. Vehicle motion or speed is measured from the drive system, e.g. axle rotation, with an odometer. Vehicle pitch is sensed with the INS. The data from the two motion sensing devices on the vehicle, one attached to the chassis the other to the body, is combined with inertial velocity and attitude information to form integrals of data that are used for observation processing by the Kalman filter. These integrals, combined with inertial position, velocity, and attitude data, are used by a Kalman filter to form corrections to the odometer error states and corrections to the navigation error states.
The output of the system is the optimally corrected inertial navigation solution. The inertial navigation solution consists of position, velocity, and attitude information for the vehicle.
Benefits and features of the invention will be obvious to one of ordinary skill in the art from the following description of the invention.